Experiments outlined in this grant proposal are designed to provide information crucial to the development of a prosthesis with potential application to a significant portion of the 200-300,000 totally deaf individuals in the U.S. In most of these deaf individuals, the acoustic nerve is at least partially intact, and experiments indicate that surviving spiral ganglion cells are electrically excitable. Simple bipolar stimulating devices have been introduced into the cochleas or acoustic nerve in a small number of patients. Psychoacoustic experiments have revealed the nature of the sensation evoked by such stimulation; physiological studies in cats have shown how the sensation is generated and encoded in the auditory nervous system; histopathologic studies have shown that at least most spiral ganglion cells survive implantation of a flexible scala tympani electrode. These studies have also shown that encoding of intelligible speech, if ever possible, will require differential, multichannel stimulation of a series of discrete, predetermined sectors of the acoustic nerve. The primary objective of these proposed experiments is to determine how and to what extent appropriately restricted sectors of the acoustic nerve might be stimulated from within the scala tympani. The effectiveness of stimulation as a function of cochlear place for different implanted stimulating electrodes will be determined in single unit colliculus experiments in which advantage is taken of the binaural response properties and cochleotopic organization of inferior colliculus neurons. A map of the response threshold to contralateral electrical stimulation can be derived by recording from a series of neurons with best frequencies collectively spanning the entire frequency spectrum (the entire length of the basilar partition.) Other experiments to be conducted concurrently will provide further crucial information about the safety of long term implantation and stimulation. If stimulation of a small number of appropriately restricted, predetermined sectors of the acoustic nerve can be effected, then it should be possible to provide information sufficient for the direct hearing of speech for subjects who are now totally deaf.